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A Meteor refuels from a Lancaster, August 1949.
Some of the earliest experiments in aerial refueling took place in the 1920s, when it was as simple as two slow-flying aircraft flying in formation, with a hose run down from a handheld gas tank on one airplane and placed into the usual fuel filler of the other. It was a very dangerous process until 1935 when brothers Fred and Al Key demonstrated the first spill-free refueling nozzle, designed by A. D. Hunter. Nowadays, specialized tanker aircraft have equipment especially designed for the task of offloading fuel to the receiver aircraft, based on Hunter's design, even at the higher speeds modern jet aircraft typically need to remain airborne.
The two most common approaches for making the union between the two aircraft are the boom and receiver system and the probe and drogue system. Much less popular was the wing-to-wing system, only used in the past.
USAF KC-135R Stratotanker, two F-15s (twin fins) and two F-16s, on an aerial refueling training mission.
The boom is a long, rigid, hollow shaft, usually fitted to the rear of the aircraft. (It almost connects the two lower aircraft in the picture at right.) It usually has a telescoping extension, a valve at the end to keep fuel in and permit it to flow, and small wings, sometimes known as ruddevators depending on design particulars (visible in picture below, in the "V" shape), to enable it to be "flown" into the receiver of the aircraft to be refueled. This receiver is fitted onto the top of the aircraft, on its centerline and usually either behind or close in front of the cockpitA cockpit was originally a pit used for cockfighting, where owners would pit fighting roosters against each other for the purpose of gambling. In 1759, the English artist William Hogarth produced a satirical print called The Cockpit showing the enthusiasm. The receiver is a round opening which connects to the fuel tanks, with a valve to keep the fuel in when not being refueled, and dust and debris out. The boom has a nozzle which fits into this opening.
USAF C-5C-5 Galaxy Description RoleHeavy strategic airlift transport Crew7 (pilot, copilot, two flight engineers, three loadmasters) Dimensions Length247. 3 m Wingspan222. 89 m Height65. 84 m Wing area6,200 sq ft576 mē Weights Empty337,937 lb153,285 kg Loaded769, approaches a KC-135R
During refueling operations, a tanker aircraft will fly in a straight and level attitude at constant speed, while the receiver takes a standard position behind and below the tanker. Modern tankers have lights which illuminate the areas outside this range, so that if the pilot can see them, he is directed to fly back towards the desired spot. Once in position, the receiver pilot flies formation with the tanker, although this can be complicated by wake turbulenceWake turbulence are vortices that are formed any time an airfoil is producing lift. Lift is generated by the creation of a pressure differential over the wing surfaces. The lowest pressure occurs over the upper surface and the highest pressure under the w. The crewman operating the boom, called a boomer or boom operator (in the USAFThe United States Air Force USAF is the aviation branch of the United States armed forces. The mission of the USAF is "to defend the United States through the control and exploitation of air and space. Organization There are three components of the USAF:, usually an enlisted sergeantThis article is about the rank of sergeant. For alternate meanings see Sergeant (disambiguation). In most non-naval military organizations, a sergeant is a non-commissioned officer (NCO) ranking above privates and corporals, and below warrant officers and), then unlatches the boom from its stowage position, and directs it towards the receiver by "flying" it with the attached wings. The telescoping section is then hydraulicallyHydraulics is a branch of science and engineering concerned with the use of liquids to perform mechanical tasks. It is part of the more general discipline of fluid power. The word "hydraulics" comes from the Greek word hydraulikos which in turn comes from extended until the nozzle fits into the receiver. When an electrical signal is passed between the boom and receiver, both valves are hydraulically opened, and pumpA pump is a mechanical device used to move liquids or gases. Also the heart is an essential pump in humans and animals to move the blood around. The earliest pump was described by Archimedes around 300 BC and is known as the Archimedes screw pump. Pumps ws on the tanker drive fuel through the shaft of the boom, and into the receiver. Once the two are mated up, additional lights on the tanker will be turned on if the receiver flies too far to one side, too low or too high, or too near or too far away, activated by sensing switchThis article is about electrical switches. For other meanings of the word "switch", see Switch (disambiguation). A switch is a device for making or breaking an electric circuit, or for selecting between multiple circuits. In the simplest case, a switch haes in the boom. When fueling is complete, the valves are closed and the boom is automatically retracted. This system is only used by the U.S. Air Force.